1. Field of the Invention
The present invention relates to a pixel circuit including three pixels to which light emitting elements which emit light of three primary colors are allocated and a power supply line for supplying current to the light emitting elements and a display apparatus wherein such pixel circuits are arranged in a matrix. More particularly, the present invention relates to a technique for reducing the number of elements which compose a pixel circuit to simplify the circuit configuration.
2. Description of the Related Art
In an image display apparatus, such as a liquid crystal display unit, a great number of liquid crystal pixels are arranged in a matrix and the transmission intensity or reflection intensity of incoming light is controlled for each pixel in accordance with information of an image to be displayed so that the image is displayed. While the displaying method just described similarly applies also to an organic EL (electroluminescence) display unit wherein organic EL elements are used as pixels or to a like apparatus, an organic EL element is a self light emitting element, different from a liquid crystal pixel. Therefore, when compared with the liquid crystal display unit, the organic EL display unit is advantageous in that the visibility of an image is high, a backlight need not be provided, the speed of response is high, and so forth. Further, the organic EL display unit is of the current controlled type wherein the luminance level (gradation) of each light emitting element can be controlled by the value of current supplied thereto. In this regard, the organic EL display unit is very different from a display unit of the voltage controlled type such as a liquid crystal display unit.
In an organic EL display unit, a simple matrix system and an active matrix system are utilized as a driving system similarly as in a liquid crystal display unit. The former system has a problem that, while it is simple in structure, it is difficult to implement a large-sized and high-definition display unit. Therefore, at present, much effort is directed to the development of organic EL display units of the active matrix system. According to the active matrix system, current to be supplied to light emitting elements in the inside of each pixel circuit is controlled by an active element (generally, thin film transistor, TFT) provided in the inside of the pixel circuit. An organic EL display unit of the active matrix system is disclosed in Japanese Patent Laid-Open No. 2003-255856, Japanese Patent Laid-Open No. 2003-271095, Japanese Patent Laid-Open No. 2004-133240, Japanese Patent Laid-Open No. 2004-029791, or Japanese Patent Laid-Open No. 2004-093682.